1. Technical Field
This invention generally relates to gyroscopes, and more specifically relates control moment gyroscopes.
2. Background Art
Control moment gyroscopes are commonly used to provide attitude control for a variety of vehicles, including spacecraft and satellites. Control moment gyroscopes normally comprise a rotor and a motor to spin the rotor about a rotor axis. The rotor is typically supported in an inner gimbal assembly and is rotated about a gimbal axis using a gimbal torque motor assembly that is attached to one end of the gyroscope. A sensor module assembly is attached to the other end of the gyroscope and is used to sense the rotational position of the inner gimbal assembly about the gimbal axis to provide for control of rotation.
The control moment gyroscope is mounted within the vehicle along the axis in which it will induce a torque. During operation of the gyroscope, the rotor is spun by a motor about its rotor axis at a predetermined rate. In order to induce a torque on the spacecraft, the gimbal torque motor rotates the gimbal assembly and the spinning rotor about the gimbal axis. The rotor is of sufficient mass and is spinning at such a rate that any movement of the rotor out of its plane of rotation will induce a significant torque around an output axis that is both normal to the rotor axis and the gimbal axis. This torque is transferred to the space craft, causing the spacecraft to move in a controlled manner.
While traditional control moment gyroscopes are generally effective, they suffer from several limitations. Many of these limitations are inherent problems that are associated with actuating the gimbal assembly around the gimbal axis. For example, traditional control moment gyroscopes have required expensive and complicated torquer motors in the torque module assembly to rotate the gimbal assembly around the gimbal axis. These motors are typically expensive precision, low ripple motors and require a complex drive train (often including a precision gear train), bearings and trunions. In addition to adding expense to the control moment gyroscope, the motor and drive train create a life limiting component that is subject to wear out and gear lubrication. Additionally, the motor and drive train can create non-linearities and resonant frequencies that limit the functional bandwidth of the gyroscope. Finally, the motor typically requires expensive high precision tachometers to detect the rate of rotation.
The sensor module assembly used to sense and control the rotation of the gimbal assembly also introduces cost and complexity to the control moment gyroscope. Typically, the sensor module requires life limiting components such as slip rings, and uses expensive single speed precision resolvers.
Additional limitations in traditional control moment gyroscopes arise from the required length of the gyroscope along the gimbal axis. Specifically, in traditional designs, the torque motor assembly and sensor module assembly are mounted on opposite ends of the gimbal axis. The addition of the torque motor assembly and sensor module assembly dramatically increase the overall length of the of the control moment gyroscope. This increase in length can be unacceptable in some dimension critical applications. The increase in length is especially problematic in applications that require multiple control moment gyroscopes to provide movement capabilities in all directions.
Thus, what is needed is an improved control moment gyroscope that overcomes the limitations of traditional designs in a low cost, effect manner.
The present invention provides a control moment gyroscope that overcomes many of the limitations of the prior art. The control moment gyroscope provides a radial actuator mechanism to provide rotation to an inner gimbal assembly around a gimbal axis. The radial actuator mechanism comprises a circular ring at the midpoint of the gimbal axis, the circular ring extending around the outer periphery of the inner gimbal assembly housing. The radial actuator mechanism rotates the inner gimbal assembly around the gimbal axis through the use of a non-contact motor that provides rotational force directly to the outer perimeter of the inner gimbal assembly. Because the inner gimbal assembly is rotated from the midpoint of the gimbal axis, a torque module assembly at the end of the gimbal axis is not required. Thus, the overall length of the control moment gyroscope can be reduced. Additionally, the cost and life limiting attributes of the torque module assembly can be eliminated, and the operational bandwidth of the gyroscope increased. Finally, because the inner gimbal assembly is rotated from the outer perimeter, the torque provided to the inner gimbal assembly is naturally increased by the leverage arm of the inner gimbal assembly.
In addition to providing rotational energy, the radial actuator mechanism can also provide rotational position sensing through an optical encoder. An optical encoder pattern is printed on a portion of the circular ring and is used by an optical sensor to provide high resolution rotation measurement. Because the rotational position is provided by the optical encoder, a sensor module assembly at the end of the gimbal axis is not required, and the overall length can be further reduced.
Additionally, the radial actuator mechanism can be used to provide power and signal delivery to the inner gimbal assembly. A low frequency AC coupler between the ring and the inner gimbal assembly can be use to deliver power to the inner gimbal assembly. A high frequency AC (e.g., radio frequency) coupler can likewise be used to deliver control signals to the inner gimbal assembly. Thus, both power and control signals can be provided to the inner gimbal assembly through the radial actuator mechanism.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.